Casillas turns 38 on May 20 and has been at Porto since 2015.
He recently put pen to paper on a new contract which sees him extend his stay at the Estadio do Dragao for an additional season.
President Pinto Da Costa praised his goalkeeper upon signing the deal.
"I'm sure it will not be his last contract, Iker has recorded that he loves this club and this city, and he has never moved for money,” he said.
Iker Casillas: The Spaniard was rushed to hospital (Image: GETTY)
Iker Casillas: The Porto goalkeeper is said to be in stable condition (Image: GETTY)
He has kept 19 clean sheets in 35 matches this season in all competitions.
Sergio Ramos offered his support to his former team mate by tweeting him prayer emojis.
Fellow goalkeeper Loris Karius also sent a message of support: "Shocked about the news! Get well soon @IkerCasillas."
According to Marca, Casillas has undergone a catheterization (inserting a catheter into a body cavity).
Invalid email
We use your sign-up to provide content in ways you've consented to and to improve our understanding of you. This may include adverts from us and 3rd parties based on our understanding. You can unsubscribe at any time. Read our Privacy Policy
Iker Casillas: The Porto goalkeeper is unlikely to feature again this season (Image: GETYY)
Porto have since released a statement to confirm the news.
"Iker Casillas suffered an acute myocardial infarction during morning practice this Wednesday, at the PortoGaia Sports Formation and Training Centre, in Olival.
"The work session was promptly interrupted so that assistance could be given to the FC Porto goalkeeper, who is at this moment at the CUP Porto Hospital. Casillas is fine, stable and with his cardiac problem resolved."